I owned a ProVari. It was rock solid performance, good battery efficiency (long life even at high voltage), and rarely ever gave me any grief. The only times it did give me grief were when my atties and cartos decided spontaneously to drop in resistance, which they are occasionally wont to do. The ProVari's mother-holding-child's-hand safety checks and amp limit prompted me to toss my atties when they dropped below 1.2 ohms (as reported by the ProVari, which I guess was accurate). Biggest drawback for me, and the reason I eventually parted with my ProVari, is that it's thick, it's long, it's heavy, and it's like vaping on a Mag Lite. If vaping on a PV you can also use to club someone with is your thing, then the ProVari is definitely a good choice. Assuming the ZMax is as reliable as a ProVari (reputation or lack thereof notwithstanding), it's still bigger than the ProVari; so I don't think I'll be getting one. YMMV though.
Now I switch among my Kicked P+ 18500 and a couple of eGo Twists. I use the P+ when I'm stationery, like when I'm at my desk at work; and my Twists when I'm driving or otherwise running around.
Interesting note about the Kick, vaping with it set to about 8.5 watts tastes and feels like vaping the ProVari set to what calculates to 10.5 - 11 watts (V²/Ω). You read many people gripe about the Kick's watt limit being only 10 watts, but 10 watts on the Kick > 10 watts on another device. It's relative. I think this is because the Kick operates directly against the battery, whereas there's some voltage loss between the guts of a ProVari and its load. Or something. I dunno. I just know vaping a 2 ohm carto at 4.7 volts (11 watts) feels like vaping that same carto on a Kicked device @ 8.5 watts.
Anyway, in most mechanical mods, if you use a Kick, you have to go down a battery size. In my Kicked P+ 18500, I have to use 18350 cells. I only get a couple of hours per battery per charge, so I'm interested in getting a small 18650 mod in which to kick some 18490 batteries -- maybe a Caravela or a Wizard's Apprentice. We'll see what happens.
But there are a few advantages of using the Kick over the variable voltage Twists. For one, there's no need to tweak the voltage if my coils vary their resistance. The Kick offers effortless consistency in my vape. For another thing, since I started building my own coils in my Penelopes, I don't have to measure or meter my resistance wire. I just eyeball it and say, "Close enough," and vape on without having to dial in the voltage.
Biggest negative to the Kick, aside from its stolen real estate forcing a smaller battery size, is its brass contacts. The contacts tarnish and must be polished from time to time. Why didn't Evolv use nickel or stainless?
There you go. There's my $0.02. Good luck in your quest!